Method and Apparatus for Providing Dual Memory Access to Non-Volatile Memory

ABSTRACT

A method and system for providing a dual memory access to a non-volatile memory device using expended memory addresses are disclosed. The digital processing system such as a computer includes a non-volatile memory device, a peripheral bus, and a digital processing unit. The non-volatile memory device such as a solid state drive can store data persistently. The peripheral bus, which can be a peripheral component interconnect express (“PCIe”) bus, is used to support memory access to the non-volatile memory device. The digital processing unit such as a central processing unit (“CPU”) is capable of accessing storage space in the non-volatile memory device in accordance with an extended memory address and offset.

PRIORITY

This application claims the benefit of priority based upon United StatesProvisional Patent Application Ser. No. 61/846,519, filed on Jul. 15,2013 in the name of the same inventor(s) and having a title of “Methodand Apparatus for Providing Dual Support of Memory Mapped andInput/Output Mapped Logical Block Address Based Access,” herebyincorporated into the present application by reference.

FIELD

The exemplary embodiment(s) of the present invention relates to digitalcomputing systems. More specifically, the exemplary embodiment(s) of thepresent invention relates to non-volatile memory devices.

BACKGROUND

A solid state drive (“SSD”) is a memory device capable of retaining datapersistently without connecting to a power supply. The SSD uses variousnon-volatile memory devices such as NAND based flash memory or phasechange memory to store data or digital information. With rapidlyincreasing storage capacity as well as access speed associated withnon-volatile memory, SSD becomes more popular for storing non-volatiledata in computing systems, such as laptop computers, desktop computers,mobile devices, tablets, servers, routers, network devices, and thelike.

A conventional flash based SSD is organized and configured to replace orsubstitute traditional hard disk drive (“HDD”) and use similar input andoutput (“I/O”) access interface as traditional non-volatile storagedrives. For example, HDD typically employs various types of I/O accessinterface, such as serial attached small computer system interface(“SAS”), serial ATA (“SATA”) interface, to handle logical block address(“LBA”) based storage access. Each block or sector of LBA, for example,can be configurable to have a storage capacity of 512 bytes.

To use similar HDD I/O access interface, conventional flash based SSDcan be configured to have a block size of 4096 bytes or 4 kilobyte(“Kbyte”) block. The flash memory typically has a minimum unit such as ablock size for a read-or-write operation at a given time. In general,the speed for flash based SSD is typically faster than HDD.

SUMMARY

One embodiment of the present invention discloses a method and/or systemto provide a dual memory access to a non-volatile memory device usingexpended memory addresses. The digital processing system such as acomputer includes a non-volatile memory device, a peripheral bus, and adigital processing unit. The non-volatile memory device such as a solidstate drive can store data persistently. The peripheral bus, which canbe a peripheral component interconnect express (“PCIe”) bus, is used tosupport dual memory access to the non-volatile memory device. Thedigital processing unit such as a central processing unit (“CPU”) iscapable of accessing storage space in the non-volatile memory device inaccordance with an extended memory address and/or offset.

Additional features and benefits of the exemplary embodiment(s) of thepresent invention will become apparent from the detailed description,figures and claims set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiment(s) of the present invention will be understoodmore fully from the detailed description given below and from theaccompanying drawings of various embodiments of the invention, which,however, should not be taken to limit the invention to the specificembodiments, but are for explanation and understanding only.

FIG. 1 is a block diagram illustrating a computer system configured toprovide dual memory access to SSD in accordance with one embodiment ofthe present invention;

FIGS. 2A-B are block diagrams illustrating exemplary systems able toimplement dual memory access via a bus in accordance with one embodimentof the present invention;

FIG. 3 is a logic flow diagram illustrating an interface between a hostand a SSD controller in accordance with one embodiment of the presentinvention;

FIGS. 4A-B are logic flows illustrating a dual memory operation showinga direct memory access and an I/O access to a SSD in accordance with oneembodiment of the present invention;

FIG. 5 is a block diagram illustrating a configuration of write memorycache used for dual memory operation in accordance with one embodimentof the present invention;

FIG. 6 is a flow diagram illustrating a write operation for a dualmemory access in accordance with one embodiment of the presentinvention;

FIG. 7 is a flow diagram illustrating a read operation performed by aprocess able to provide a dual memory access in accordance with oneembodiment of the present invention;

FIG. 8 is a flowchart illustrating a pre-fetch operation performed by aprocess which is able to provide a dual memory access in accordance withone embodiment of the present invention;

FIG. 9 is a flowchart illustrating a dual memory access to a SSD inaccordance with one embodiment of the present invention;

FIG. 10 is a diagram illustrating a computer network capable ofproviding network traffic routing between various users using a dualmemory access in accordance with one embodiment of the presentinvention; and

FIG. 11 is a block diagram illustrating a digital processing systemcapable of implementing dual memory access in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention are described herein with contextof a method and/or apparatus for enabling a digital processing unit todirectly access memory space in a solid state drive (“SDD”).

The purpose of the following detailed description is to provide anunderstanding of one or more embodiments of the present invention. Thoseof ordinary skills in the art will realize that the following detaileddescription is illustrative only and is not intended to be in any waylimiting. Other embodiments will readily suggest themselves to suchskilled persons having the benefit of this disclosure and/ordescription.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be understood that in the development of any such actualimplementation, numerous implementation-specific decisions may be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be understood that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skills in the art having the benefit of embodiment(s) of thisdisclosure.

Various embodiments of the present invention illustrated in the drawingsmay not be drawn to scale. Rather, the dimensions of the variousfeatures may be expanded or reduced for clarity. In addition, some ofthe drawings may be simplified for clarity. Thus, the drawings may notdepict all of the components of a given apparatus (e.g., device) ormethod. The same reference indicators will be used throughout thedrawings and the following detailed description to refer to the same orlike parts.

The term “system” or “device” is used generically herein to describe anynumber of components, elements, sub-systems, devices, packet switchelements, packet switches, access switches, routers, networks, computerand/or communication devices or mechanisms, or combinations ofcomponents thereof. The term “computer” includes a processor, memory,and buses capable of executing instruction wherein the computer refersto one or a cluster of computers, personal computers, workstations,mainframes, or combinations of computers thereof.

One embodiment of the present invention discloses a digital processingsystem which can be a computer, server, or network router capable ofproviding a dual memory access to a non-volatile memory device usingexpended memory addresses. The digital processing system includes anon-volatile memory device, a peripheral bus, and a digital processingunit. The non-volatile memory device such as a SSD can store datapersistently. The peripheral bus, which can be a peripheral componentinterconnect express (“PCIe”) bus, is used to support memory access tothe non-volatile memory device. The digital processing unit such as acentral processing unit (“CPU”) is capable of accessing storage space inthe non-volatile memory device in accordance with an extended memoryaddress and/or offset.

FIG. 1 is a block diagram 100 illustrating a computer system configuredto provide dual memory access to SSD 106 via a peripheral bus 108 inaccordance with one embodiment of the present invention. Diagram 100illustrates a non-volatile (“NV”) memory device or SSD 106, a peripheralbus 108, a digital processing unit or CPU 102, a bus controller 110, anda memory 104. It should be noted that the underlying concept of theexemplary embodiment(s) of the present invention would not change if oneor more blocks (or devices) were added to or removed from diagram 100.

NV memory device or SSD 106 is able to store data or informationpersistently without connecting to an electrical power supply. The NVmemory, for example, can be flash memory, phase-change memory, ormagnetoresistive random-access memory (“MRAM”). NV memory device 106, inone embodiment, is flash memory based SSD.

The flash memory based SSD, for example, includes multiple arrays ofNAND based flash memory cells for storage. The flash memory, whichgenerally has a read latency less than 100 microseconds (“μs”), isorganized in a block device wherein a minimum access unit may be set toeither four (4) Kbyte, eight (8) Kbyte, or sixteen (16) Kbyte memorycapacity depending on the flash memory technology. Other types of NVmemory, such as phase change memory (“PCM”), magnetic RAM (“MRAM”),STT-MRAM, or ReRAM, can also be used. As NV memory evolves such asReRAM, byte addressable NV memory such as PCM or MRAM (Magnetic RAM) areavailable for storage and access. To simplify the forgoing discussion,the flash memory or flash based SSD is herein used as an exemplary NVmemory for dual memory access.

Peripheral bus 108 which couples to the NV memory device is configuredto facilitate memory access to SSD 106 based on extended memory address.In one embodiment, peripheral bus 108 is a peripheral componentinterconnect express (“PCIe”) bus which is capable of facilitatingmemory access to SSD 106 using memory addresses such as an address for aword or a byte. Word size, for example, can be one (1) byte, two (2)bytes, four (4) bytes, and/or sixteen (16) bytes.

CPU or central processing unit 102 is a microprocessor, processor, orcontroller capable of executing computing instructions to carryoutvarious operations. To simplify forgoing discussion, CPU will be used torefer to central processing unit, microprocessor, processor,microcontroller, digital signal processing component, and the like. CPU102, in one embodiment, is configured to directly access at least aportion of the storage space in SSD 106 in accordance with a set ofextended memory address and/or offset. For example, CPU 102 uses a setof predefined extended memory address to access a section of SDD asstorage class memory (“SCM”). To improve access latency, a bufferingmechanism and/or a pre-fetch operation can be implemented to mitigateaccessing speed relating to NV memory.

Memory 104, in one example, is a dynamic random access memory (“DRAM”)that stores information such as instructions, programs, and data forspeedy memory access. Memory 104 generally provides fast turn-aroundtime. The information stored in memory 104 is usually volatile, and thestored information disappears as soon as memory 104 disconnects frompower.

The computer system further includes an architecture of cache schemesuch as level 1 (“L1”), L2, L3, and/or unique cache or buffer memories.A dedicated cache memory, in one embodiment, is assigned to implementSCM for reducing access latency. For example, a unique caching schemefor dual mode access can be developed based on types of NV memory used.Depending on the applications, the cache scheme which is also referredto as buffers can be at L1, L2, L3, or specially allocated memory space.A buffer, in one example, can buffer or temporarily store digitalinformation between peripheral bus 108 and CPU 102.

Bus controller 110, also known as bus interface, is coupled withperipheral bus 108 for facilitating and/or assisting functions relatingto dual memory access. Note that a function of dual memory access is toprovide direct memory access to the NV memory device. Another functionof dual memory access is to provide a function of I/O storage capable ofaccessing SSD 106 as an I/O device. In one embodiment, bus controller110 is configured to work in conjunction with CPU 102 and bus 108 toprovide functions of the dual memory access to SSD 106.

In operation, when an instruction 130 is fetched from instruction set126, CPU 102 identifies various fields such as fields for operation code(“op code”) 112 and memory address 132. Memory address 132, in oneembodiment, includes memory addresses 114 and extended memory addresses116. It should be noted that instruction 130 may include other fields118 which may include offset and/or other addresses. CPU 102, in oneembodiment, is able to access memory 104 using direct memory address 114as indicated by arrow 120, and access SSD 106 using extended memoryaddress 116 as indicated by arrow 122.

An advantage of using the dual memory access is that it allows aprocessor to directly access at least a portion of the memory space inSSD.

FIG. 2A is a block diagram 200 illustrating an exemplary system that isable to provide dual memory access to SSD via bus 108 in accordance withone embodiment of the present invention. Diagram 200 illustrates adigital processing system including SSD 206, peripheral bus 108, CPU102, bus controller 110, I/O controller 202, and memory 104. Diagram 200is similar to diagram 100 except that SSD 206 is partitioned. In oneembodiment, SSD 206 allocates a memory portion 210 that can be accessedby direct memory access or direct memory map as indicated by arrow 122.SSD 206 also includes a second section 212 for I/O storage. SSD 206 iscoupled to I/O controller 202 for managing I/O access.

During an operation, the system can access memory portion 210 accordingto extended memory address 116. CPU 102 can also access I/O storage 212of SSD 206 using virtual address 208 via I/O controller 202. It shouldbe noted that a unique cache, not shown in FIG. 2A, can be situatedbetween CPU 102 and memory portion 210 for enhancing efficiency of NVmemory access. In one embodiment, I/O controller 202 is configured toprovide both memory access and I/O access in view of bus configuration.

To support dual memory access, a bus interface switch such as PCIe isused to map memory access to I/O mapped device. For memory access suchas read modify write, memory address associated with PCIe, for example,may be configured and mapped to I/O LBA address(s). Note that writecache (or buffer) and/or read buffer (or cache) may be used for memoryaccess. To reduce access latency, read cache and/or special pre-fetchmechanism may be implemented to enhance overall system performance.

It should be noted that with evolution of NV memory technology, the readand write latency of NV memory has been improved. To benefit theimprovement of access speed associated with the NV memory, CPU 102 candirectly access at least a portion of the NV memory (or SSD 210) as amemory instead of an I/O device. To map memory address to LBA of SSD,PCIe bus 108 is able to handle such memory map in SSD 206 through I/Ocontroller. It should be noted that peripheral bus 108 such as PCIesupports both memory access and I/O access.

SSD 206 or other NV memory based storage, in one example, can be locatedor attached to a PCIe bus interface or a host memory interface thatsupports memory based addressing and I/O block level driver access. Theaddress scheme of memory space and the I/O block level scheme can bedetermined from the following equation, Memory address=LBA*Blocksize+offset address in the block.

If, for example, the block size equals to 4 KByte and offset is 356 insecond LBA, Memory address can be identified with 1*4096+356=4452 Byte.LBA can be derived from the following equation,

LBA=INT (Memory address/LBA size)

Where INT is the integer function. Offset=MOD (Memory address/LBA size)where MOD is the modular function.

FIG. 2B is a block diagram 250 illustrating an alternative exemplarysystem capable of providing dual memory access in accordance with oneembodiment of the present invention. Diagram 250 illustrates a digitalprocessing system including SSDs 252-254, peripheral bus 108, CPU 102,bus controller 110, I/O controller 202, and memory 104. Diagram 250 issimilar to diagram 200 except that two (2) SSDs 252-254 are used in thesystem. In one aspect, SSD 252 is dedicated to direct memory access viamemory map. SSD 254 is used for I/O storage which can be accessed as anI/O device via I/O controller 202. It should be noted that duel mappingprovides compatibility of conventional NV memory drives such as SSD,HDD, magnetic types, and/or optical drive via I/O access or traditionaldirect memory access.

An advantage of using the dual memory access is that it can be effectivefor big data application because dual memory access allows CPU to havemore control over SSD. For example, when large database is stored inSSD, SCM can be used to provide direct memory access to SSD. It shouldbe noted that with improvement of NV memory technology such as PCM orReRAM, the read and write memory access can have finer granularity suchas byte access or word access. To facilitate memory access with finergranularity, PCIe memory space access can be used by SCM.

FIG. 3 is a logic flow diagram illustrating an interface between a hostand a SSD controller in accordance with one embodiment of the presentinvention. The interface can be defined or specified according to astandard interface specification such as NV memory express (“NVMe”) forimplementing one embodiment of dual memory access. NVMe, as an exemplarystandard, is a register level interface that allows host software tocommunicate with a NV memory subsystem such as SSD. The interfaceprovides optimization between enterprise and client SSDs connected byPCIe interface. It should be noted that the interface for facilitatingmemory access may use block based concept such as LBA for SSD access. Tosimplify forgoing discussion, NVMe is used as an exemplary interfacestandard. It should be noted that other similar standard will also workfor SSD dual memory access.

According to NVMe, various steps are generally required to complete dataor information exchange between a host and a controller of NV memory. Instep 1, the host issues a write command which is submitted and queued ata submission queue. After sending a doorbell signal by the hostindicating a new command at step 2, the controller, at step 3, fetchesthe write command from the submission queue. After executing the writecommand at step 4, the controller, at step 5, writes completinginformation which is queued at a completion queue. The completinginformation may indicate the most recent sequential queue (“SQ”) thathas been fetched. After receiving an interrupt signal ormessage-signaled interrupt (“MSI”) from the controller, the host obtainsand processes the completion entry at step 7. The host subsequentlywrites a doorbell to release the completion entry at step 8.

FIG. 4A is a logic flow 400 illustrating a dual memory operation showinga direct memory access and an I/O access to a SSD in accordance with oneembodiment of the present invention. Logic flow 400 includes an I/Oaccess flow 406 and a memory access flow 408. It should be noted thatthe underlying concept of the exemplary embodiment(s) of the presentinvention would not change if one or more layers (or blocks) were addedto or removed from flow 400.

During execution of application 410, a logic flow 406 is followed whenthe system issues a command for I/O storage operation. Alternatively, alogic flow 408 is executed when the system issues a direct memory accessto NV memory 420. For logic flow 406, file system 412 is used to handlecommunication between application executed by CPU and block devicedriver 414. In one example, block device driver 414 is NV memorydependent. Block device driver 414 may reside at the I/O interface orI/O controller. A translation layer 418 such as flash translation layer(“FTL”), in one aspect, is used to facilitate communication betweenblock device driver 414 and NV flash memory 420. Note that FTL 418 mapsLBAs to physical addresses.

To simplify implementation of NV memory operation, FTL 418 provides aninterface mapping between logical addresses and physical addresses. Afunction of FTL 418 is to translate between LBA and physical pageaddress (“PPA”). PPA addressed by LBA, in one embodiment, points to apage in a flash memory. Depending on the applications, PPA may also beconfigured to point to a sector or a portion of a page in a flashmemory.

SSD or NV flash memory 420, in one example, is handled by software orhardware as I/O device controlled by block device driver 414. Thehardware adds FTL 418 to translate LBA to PPA or vice verse. In someinstances, storage access to SSD via I/O access is mapped throughvirtual paging mechanism.

Memory access flow 408, in one aspect, illustrates a direct memoryaccess to NV flash memory 420 via a memory cache or buffer 416. Itshould be noted that LBA and memory address translation are implementedin dual mapping mode. An advantage of providing a dual mapping mode ordual memory access which includes I/O device and direct memory access isthat the dual module continues to support the traditional I/O accessmodel such using NVM express protocol. Also, SSD has a memory addressspace that can be accessed by CPU for storing information.

FIG. 4B is a logic flow 402 illustrating a dual memory operation showinga direct memory access to SSD in accordance with one embodiment of thepresent invention. Flow 402 is similar to flow 408 shown in FIG. 4Aexcept that flow 402 show a direct memory access portion of the logicsequence. In one embodiment, when an application 450 is executed,application 450 is able to access data or information stored in NVmemory 420 via memory cache 416 and FTL 418. It should be noted thatcache 416 is a special dedicated buffer or a group of buffers configuredto handle various read-write and/or pre-fetch operations.

FIG. 5 is a block diagram 500 illustrating a configuration of writememory cache used for dual memory access in accordance with oneembodiment of the present invention. Diagram 500 includes a cache 502and multiple buffers 508 wherein cache 502 includes at least one bufferlist 518. Buffer list 518, in one example, includes a head pointer 520and a tail pointer 522. Pointers 520-522 indicate used buffers as wellas free buffers. The terms “buffer” and “cache”, which can be usedinterchangeably, refer to a small block of volatile memory or DRAM. Itshould be noted that the underlying concept of the exemplaryembodiment(s) of the present invention would not change if one or moreblocks (or devices) were added to or removed from diagram 500.

Cache 502, in one example, includes 4 KByte memory space used for bufferunit map. A function of memory cache is to reduce the write latency bysupporting write back cache mode. Buffers 506 are actual buffers wherethe content of each buffer will be stored in SSD when it is ready to bestored. The cache or buffer, in one example, is used to absorb the delayduring a write-to-memory operation. Before writing to a block of SSD,data or information to be written is gathered in a buffer or written toa buffer first. When the buffer is full or almost full, the content ofbuffer is rewritten to SSD.

Memory cache 502-506 can also be used as read cache or buffer in whichthe read access latency during SSD read operation can be reduced. Cache502-506 can also be used to support pre-fetch operation in whichpotential data or information is preloaded from the NV memory (or SSD)to buffer 506.

An advantage of using buffers or cache is that buffering datatransmission between CPU and SSD can mitigate access latency.

The exemplary embodiment of the present invention includes variousprocessing steps, which will be described below. The steps of theembodiment may be embodied in machine or computer executableinstructions. The instructions can be used to cause a general purpose orspecial purpose system, which is programmed with the instructions, toperform the steps of the exemplary embodiment of the present invention.Alternatively, the steps of the exemplary embodiment of the presentinvention may be performed by specific hardware components that containhard-wired logic for performing the steps, or by any combination ofprogrammed computer components and custom hardware components.

FIG. 6 is a flow diagram 600 illustrating a write process for a dualmemory access in accordance with one embodiment of the presentinvention. At block 602, a memory write operation is issued. Forexample, a memory access by a central processing unit or CPU for writinginformation is issued to a first storage location addressed by anexpanded memory address. Based on the expanded memory address, acontroller is able to identify that the first storage location is inSSD. The process, at block 604, examines the buffer list to see whetherthe expanded memory address is in a buffer. If the buffer is not foundor absent from the buffer list, the process proceeds to block 606 tocheck whether a new buffer or free buffer is available. If a new bufferis available, the process proceeds to block 608. Otherwise, the processproceeds to block 610.

At block 610, a buffer is identified or picked as a new buffer based ona predefined buffer identifying procedure or mechanism. At block 612,the content from a block pointed by a LBA associated with the new bufferis read. After merging the content or block content with the contentcurrently in the identified buffer as new buffer at block 614, themerged content is written or rewritten back to the NV memory at block616. A free buffer signal indicating available new buffer or free bufferis sent. The process subsequently goes to block 606.

If the buffer is found in the buffer list at block 604, the processproceeds to block 608 and the information is written to the buffer. Atblock 618, if the buffer is not full, the process loops back to block602 to process the next write operation. Otherwise, the process proceedsto block 620 and transmits the information or content from the cache tothe first storage location of the flash memory SSD. At block 622, thebuffer is free after the content is written to SSD.

The process is also able to issue an I/O access to an I/O controller forwriting data to a second storage location in the flash memory based SSD.Note that the data is stored to a second location of the flash memorySSD in accordance with an LBA. The second location of SSD is assignedfor handling I/O access. It should be noted that a FTL is used tocommunicate between CPU and SSD.

Depending on the applications, different mechanisms of buffer reuse,renew, or deletion can be applied. For example, when a write-cache orbuffer is getting full, either an earliest written buffer or the leastfrequently written buffer is written to NV memory. Before writing to theNV memory, the same 4 KByte of data from the NV memory is first read andsubsequently merged with the content of the buffer. After merging, thebuffer is free once the merged data is written to the NV memory. Itshould be noted that different criteria to choose which 4 Kbyte ofbuffer to be freed or updated depends on the applications.

Also, a least frequently write-hit buffer or cache can also be used asalternative criteria to choose a buffer to be cleared.

FIG. 7 is a flow diagram 700 illustrating a read operation performed bya process able to provide a dual memory access in accordance with oneembodiment of the present invention. During a read operation, a bufferor read memory cache is used to enhance efficiency of SSD read. At block702, when a memory read is applied from a host CPU, the associatedmemory address is converted to the LBA according to page or block size.At block 704, a process searches the buffer list to examine whether therequested content addressed by the memory address already exists in thebuffer list. At block 706, if the requested content addressed by thememory address is not in the buffer list, the content of the bufferaddressed by the memory address is read from the NV memory at block 708.The process subsequently proceeds to block 710.

At block 706, if the memory address matches with one of buffer's LBA onthe buffer list, the content of buffer is read from the cache buffer atblock 710. At block 712, the read data is returned to the host CPU. Theread operation is subsequently ended. It should be noted that theunderlying concept of the embodiment(s) of read operation should notchange if some steps and/or sequences are inserted, replaced, and/orremoved.

FIG. 8 is a flowchart 800 illustrating a pre-fetch operation performedby a process which is able to provide a dual memory access in accordancewith one embodiment of the present invention. Since NV memory generallyhas larger access latency than DRAM, a pre-fetch operation isimplemented to shorten such latency. In one embodiment, a pre-fetchmechanism is implemented by software using the corresponding buffer orcache scheme. Once data is pre-fetched, the host CPU can read the datafrom the corresponding buffer. At block 802, a process issues apre-fetch command. For example, a special local cache command issues apre-fetch or read a portion of SSD based on identified LBAs. At block804, the process checks to see if the data to be pre-fetched is alreadyin the cache or buffer. If the data to be pre-fetched is not in thebuffer, the process activates SSD controller to read the data from SSDto the buffer at block 806. The process proceeds to block 808.

At block 808, if the data to be pre-fetched is in the buffer, theprocess proceeds to read the data from the buffer as indicated by thememory address. At block 810, the process returns the read data to thehost CPU as it requested earlier. The pre-fetch operation subsequentlyends.

A pre-fetch command, for example, can be defined based on vendorspecific command field. The pre-fetch command allows software driver toautomatically issue pre-fetch command based on user's preference. Uponreceipt of a pre-fetch command, SSD controller proceeds to read LBA datato a DRAM buffer which will be ready for access by host.

FIG. 9 is a flowchart 900 illustrating a dual memory access to a SSD inaccordance with one embodiment of the present invention. At block 902, aprocess capable of providing dual mode memory access issues a directmemory access by a central processing unit to read information stored ata first storage location addressed by an expanded memory address. In oneembodiment, the range of expanded memory address can be substantiallylarger than DRAM memory address whereby the expended memory address isautomatically mapped into SSD memory space. At block 904, uponidentifying the first storage location in a flash memory SSD inaccordance with the expanded memory address, the information stored inthe first storage location is fetched from the flash memory SSD to acache. In one example, a pre-fetch instruction or command to preload aportion of data from the flash memory SSD can be issued. Note thatpre-fetch is to reduce memory access latency. At block 908, theinformation is read from the cache and forwarded to the host.

In one aspect, the process also issues an I/O access for reading datastored at a second storage location in the flash memory SSD. It shouldbe noted that the data from the second location of the flash memory SSDis obtained in accordance with a logical block address (“LBA”).

FIG. 10 is a diagram illustrating a computer network 1000 capable ofproviding network traffic routing between various users using a dualmemory access in accordance with one embodiment of the presentinvention. In this network environment, electronic band 1001 can becoupled to a wide-area network 1002. Wide-area network 1002 includes theInternet, or other proprietary networks including America On-Line™, SBC,Microsoft Network™, and Prodigy™. Wide-area network 1002 may furtherinclude network backbones, long-haul telephone lines, Internet serviceproviders, various levels of network routers, and other means forrouting data between computers.

Server 1004 is coupled to wide-area network 1002 and is, in one aspect,used to route data to clients 1010-1012 through a local-area network(“LAN”) 1006. Server 1004 is coupled to SSD 106 wherein server 1004 canbe configured to provide dual memory access. The LAN connection allowsclient systems 1010-1012 to communicate with each other through LAN1006. Using conventional network protocols, USB portable system 1030 maycommunicate through wide-area network 1002 to client computer systems1010-1012, supplier system 1020 and storage device 1022. For example,client system 1010 is connected directly to wide-area network 1002through direct or dial-up telephone or other network transmission lines.Alternatively, clients 1010-1012 may be connected through wide-areanetwork 1002 using a modem pool.

Having briefly described one embodiment of the computer network in whichthe embodiment(s) of the present invention operates, FIG. 11 illustratesan example of a computer system 1100, which can be a server, a router, aswitch, a node, a hub, a wireless device, or a computer system.

FIG. 11 is a block diagram illustrating a central processing systemcapable of implementing dual memory access in accordance with oneembodiment of the present invention. Computer system or a signalseparation system 1100 can include a processing unit 1101, an interfacebus 1111, and an input/output (“IO”) unit 1120. Processing unit 1101includes a processor 1102, a main memory 1104, a system bus 1111, astatic memory device 1106, a bus control unit 1105, a SSD as massstorage memory 106, and a signal separation access unit 1109. It shouldbe noted that the underlying concept of the exemplary embodiment(s) ofthe present invention would not change if one or more blocks (circuit orelements) were added to or removed from diagram 1100.

Bus 1111 is used to transmit information between various components andprocessor 1102 for data processing. Processor 1102 may be any of a widevariety of general-purpose processors, embedded processors, ormicroprocessors such as ARM® embedded processors, Intel® Core™ Duo,Core™ Quad, Xeon®, Pentium microprocessor, Motorola™ 68040, AMD® familyprocessors, or Power PC™ microprocessor.

Main memory 1104, which may include multiple levels of cache memories,stores frequently used data and instructions. Main memory 1104 may beRAM (random access memory), MRAM (magnetic RAM), or flash memory. Staticmemory 1106 may be a ROM (read-only memory), which is coupled to bus1111, for storing static information and/or instructions. Bus controlunit 1105 is coupled to buses 1111-1112 and controls which component,such as main memory 1104 or processor 1102, can use the bus. Bus controlunit 1105 manages the communications between bus 1111 and bus 1112. Massstorage memory or SSD 106, which may be a magnetic disk, an opticaldisk, hard disk drive, floppy disk, CD-ROM, and/or flash memories areused for storing large amounts of data.

I/O unit 1120, in one embodiment, includes a display 1121, keyboard1122, cursor control device 1123, and communication device 1125. Displaydevice 1121 may be a liquid crystal device, cathode ray tube (“CRT”),touch-screen display, or other suitable display device. Display 1121projects or displays images of a graphical planning board. Keyboard 1122may be a conventional alphanumeric input device for communicatinginformation between computer system 1100 and computer operator(s).Another type of user input device is cursor control device 1123, such asa conventional mouse, touch mouse, trackball, or other type of cursorfor communicating information between system 1100 and user(s).

Communication device 1125 is coupled to bus 1111 for accessinginformation from remote computers or servers, such as server 104 orother computers, through wide-area network 102. Communication device1125 may include a modem or a network interface device, or other similardevices that facilitate communication between computer 1100 and thenetwork. Computer system 1100 may be coupled to a number of servers 104via a network infrastructure such as the infrastructure illustrated inFIG. 11.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this exemplary embodiment(s) of the presentinvention and its broader aspects. Therefore, the appended claims areintended to encompass within their scope all such changes andmodifications as are within the true spirit and scope of this exemplaryembodiment(s) of the present invention.

What is claimed is:
 1. A digital processing system, comprising: anon-volatile memory device configured to store data persistently; aperipheral bus coupled to the non-volatile memory device and configuredto support memory access to the non-volatile memory device; and adigital processing unit coupled to the peripheral bus and able to accessat least a portion of storage space in the non-volatile memory device inaccordance with extended memory address and offset.
 2. The system ofclaim 1, further includes a cache coupled to the digital processing unitand able to buffer information between the peripheral bus coupled withthe non-volatile memory device and the digital processing unit.
 3. Thesystem of claim 1, further includes a bus interface coupled to theperipheral bus and configured to provide a function of dual memoryaccess capable of facilitating direct memory access to the non-volatilememory device.
 4. The system of claim 3, wherein the bus interface isconfigured to provide a function of input/output (“I/O”) storage accessable to access data to a portion of the non-volatile memory device viaI/O access.
 5. The system of claim 1, wherein the non-volatile memorydevice is one of flash memory, phase-change memory, and magnetoresistiverandom-access memory (“MRAM”).
 6. The system of claim 1, wherein thenon-volatile memory device is a flash memory solid state drive (“SSD”)includes an address translation component able to provide a function offlash translation layer.
 7. The system of claim 1, wherein theperipheral bus is a peripheral component interconnect express (“PCIe”)bus capable of facilitating word addressable memory access to thenon-volatile memory device.
 8. The system of claim 1, wherein thedigital processing unit is configured to access at least a portion offlash memory solid state drive (“SSD”) as storage class memory.
 9. Thesystem of claim 1, wherein the digital processing unit is able topre-fetch information stored in a flash memory solid state drive (“SSD”)to reduce access latency.
 10. A method for providing dual mode memoryaccess, comprising: issuing a direct memory access by a digitalprocessing unit for reading information stored at a first storagelocation addressed by an expanded memory address; identifying the firststorage location in a flash memory solid state drive (“SSD”) inaccordance with the expanded memory address; fetching the informationstored in the first storage location from the flash memory SSD to acache; and reading the information from the cache.
 11. The method ofclaim 10, comprising issuing an input/output (“I/O”) access for readingdata stored at a second storage location in the flash memory SSD. 12.The method of claim 11, comprising obtaining the data from the secondlocation of the flash memory SSD in accordance with a logical blockaddress (“LBA”).
 13. The method of claim 10, wherein fetching theinformation stored in the first storage location includes issuing apre-fetch instruction to preload a portion of data from the flash memorySSD to reduce memory access latency.
 14. The method of claim 10, furthercomprising communicating with the flash memory SSD via a flashtranslation layer.
 15. A method for providing dual mode memory access,comprising: issuing a memory access by a digital processing unit forwriting information to a first storage location addressed by an expandedmemory address; identifying the first storage location in a flash memorysolid state drive (“SSD”) in accordance with the expanded memoryaddress; writing the information to a cache which is situated betweenthe digital processing unit and the flash memory SSD; and transmittingthe information from the cache to the first storage location of theflash memory SSD.
 16. The method of claim 15, comprising issuing aninput/output (“I/O”) access to an I/O controller for writing data to asecond storage location in the flash memory SSD.
 17. The method of claim16, comprising storing the data to the second location of the flashmemory SSD in accordance with a logical block address (“LBA”).
 18. Themethod of claim 15, further comprising communicating with the flashmemory SSD via a flash translation layer.
 19. The method of claim 15,wherein writing the information to a cache includes, searching a bufferlist to determine whether the cache is on the buffer list; requesting anew buffer for cache space if the cache is absent on the buffer list;identifying the new buffer in accordance with a predefined mechanismwhen free buffer space is not available; reading block content from ablock pointed by a logic block address (“LBA”) which is associated withthe new buffer; merging the block content with cache content currentlyin the new buffer and writing merged content to the non-volatile memory;and issuing a free buffer signal indicating availability of the newbuffer.
 20. The method of claim 15, wherein transmitting the informationfrom the cache to the first storage location of the flash memory SSDincludes continuing next writing if current memory buffer has additionalstorage space.